Iran has long insisted its program is peaceful, though it is the only non-nuclear-armed nation enriching uranium at that level. The U.S., the IAEA and others say Iran had a nuclear weapons program up until 2003.

The clash over Iran's nuclear program is escalating, with U.S. sanctions and Europe's snapback threat putting Tehran under maximum pressure.

German Foreign Minister Johann Wadephul confirmed talks next week and warned Iran that sanctions would snap back into effect unless it reached a verifiable and durable deal to def